Lecture 17 - Exercises

17A - Dictionaries

Write the output of the following program. If a line causes an error, write ERROR at that point in the output and continue on with the program as if the line causing the error had been skipped.

phone_book = {"Wehrwein": 6324}
phone_book["Ahmed"] = 2624
phone_book["Jagodzinski"] = 6160
phone_book["Fizzano"] = 3807
phone_book["Wehrwein"] = 6327

print(phone_book["Wehrwein"])
print(phone_book["Fizzano"])
print(phone_book["Liu"])
print(phone_book.get("Wehrwein"))
print(phone_book.get("Liu", 9999))
print("6327" in phone_book)
print("Wehrwein" in phone_book)
print("Wehrwein" in phone_book.items())

del phone_book["Jagodzinski"]

contents = []
for k in phone_book.keys():
    contents.extend([k, phone_book[k]])
print(len(contents))

print(contents[-1])

Problems

1. Implement the following function:

   def charcount(in_string):
       """ Return a dictionary that maps each unique character in 
       in_string to the number of times it appears in the string.
       Precondition: in_string is a string
       Example: count("hahah") # => {"a": 2, "h": 3} """   

2. Implement the following function; you may call the function you wrote for Problem 1.

   def strmode(in_str):
       """ Return the most frequently-appearing character in   
       in_str, or any of the most frequent characters in case of a
       tie. Precondition: in_str is a string with nonzero length.
       Examples: strmode('hahah') # => 'h'
                 strmode('who') # => could return 'w', 'h', or 'o'
       """

3. Implement the following function:

   def dict_intersection(d1, d2):
     """ Return a dictionary containing only keys that appear in both d1 and d2.
     Each key's value is the sum of the corresponding values in d1 and d2.
     Example: dict_intersection({1: 2, 2: 3}, {2: -1, 3: 10}) => {2: 2}"""

4. Implement the following function:

   def same_elements(list1, list2):
     """Return true if list1 and list2 contain exactly the same elements, possibly
     in a different order from each other. 
     Examples: same_elements([1, 2], [1, 2]) => True
               same_elements([1, 2], [2, 1]) => True
               same_elements([1, 2, 3], [2, 1, 3]) => True
               same_elements([1, 2], [2, 2]) => False
               same_elements([1, 1, 2], [2, 1, 1]) => True
               same_elements([1, 2, 2], [1, 1, 2]) => False
     Precondition: list1 and list2 are lists """